1. Field of the Invention
Most writing instruments include a tank for pooling ink in order to allow writing to be performed for a long period of time. Some of them are provided with an ink introducing tube for feeding only a sufficient amount of ink from an ink tank to a writing point (nib, ballpoint, plastic tip, etc.).
The present invention relates to an ink introducing tube for introducing ink pooled in an ink tank to a writing point, and to a writing instrument incorporating the ink introducing tube therein.
2. Description of the Related Art
Conventional writing instruments include, for example, a fountain pen which may be refilled by replacing a spare ink tank (cartridge) storing fluid ink.
In a writing pen 1 shown in FIG. 5, a rigid intermediate member 3 is fixed in a central interior portion of a tubular housing 2, and an ink introducing tube 4 supported by the intermediate member 3 is held by a tubular inner cotton member 5 arranged in front of the intermediate member 3. Further, the ink introducing tube 4 is coupled to a writing nib 6 at the front portion of the inner cotton member 5. On the other hand, an ink tank holding tube body 7 having a protrusion 7A is formed in the rear end portion of the intermediate member 3, and a cartridge type ink tank 8 is inserted in the ink tank holding tube body 7, thus enabling writing to be performed. Also, the rear end of the ink introducing tube 4 is projected into the ink tank holding tube body 7 so that it comes into contact with the ink within the ink tank. As shown in FIG. 6, in cross section, the ink introducing tube 4 has 8 slit-like ink introducing grooves 4A that radially extend from the center.
The ink introducing tube 4 allows ink to flow toward the direction of the nib by capillary action of the slits. Due to the capillary action, the ink thus supplied is impregnated into the inner cotton member 5 in both the radial and axial directions so that it is retained in the cotton member 5. Further, the ink introducing tube 4 is formed such that greater capillary action is exerted on the nib 6 side than on the intermediate member 3 side in the axial direction of the pen. The ink supplied from the ink introducing tube 4 moves to the nib 6 formed of a porous felt member, a sintered synthetic resin, or the like. At this time, any surplus ink is absorbed by the inner cotton member 5 at the coupling portion.
When writing is performed with the above-described writing pen 1, as ink is consumed, the ink transfers from the ink tank 8 to the nib side due to the capillary action exerted by the slits 4A. At this time, since the ink tank 8 is in a closed state except for the ink introducing tube 4, outflow of ink does not take place unless the ink within the ink tank is replaced by air from the outside. That is, air corresponding to the amount of used ink enters into the ink tank 8 through the nib 6 and the ink introducing tube 4, thus balancing the pressure with the outside. However, if the interchange of air with the ink does not take place in a satisfactory manner, the pressure within the ink tank 8 becomes low so that the ink drops less easily, leaving skips in drawn ink lines. Conversely, if the air within the ink tank 8 rapidly expands when the amount of air inside the ink tank 8 is already increasing, more ink is pushed out in correspondingly greater force, causing sudden thickening of drawn letters or ink blobbing.
In view of the above, in order to enable a relatively large amount of ink to be supplied from the ink tank 8, an attempt was made to cause the capillary action to take place at various many locations by using the ink introducing tube 4 having a construction such as shown in FIG. 7. That is, the ink introducing tube 4 is formed having a cross section in which protrusions are formed from the outer periphery toward the inner periphery thereof (i.e., by being extended to the vicinity of the center), thus increasing the total area of the slits formed therebetween. Note that the slit width of the protrusion is set to 50 microns at a section Axe2x80x94A, and a central space C is set to approximately the same value. Although this allows an increase in the amount of ink retained in the ink introducing tube 4, the ink retained in the slits obstructs movement of air to the ink tank 8, so that air does not enter into the ink tank 8, resulting in extremely poor ink ejection.
On the other hand, as shown in FIG. 8, as an attempt to allow a large amount of air to enter into the ink tank 8 more easily, the cross section of the ink introducing tube 4 is formed such that protrusions each having a small height are projected toward the central portion, with wider intervals being set therebetween. That is, the width of the space Bxe2x80x94B capable of capillary action which is formed by the protrusions having a small height is set to 100 microns, and the central space C is set to approximately the same value. In this case, the replacement of ink in the ink tank 8 by air from the outside is performed extremely easily, with a result that excessive outflow of ink becomes liable to occur to cause writing unevenness.
The present invention has been made based on the above findings, and an object thereof is to provide an ink introducing tube in which air can be easily introduced into an ink tank and also excellent ink flowing action that is suitable for writing can be attained, and a writing instrument incorporating the ink introducing tube therein.
In order to attain the above object, a first aspect of the present invention relates to an ink introducing tube for introducing ink from an ink tank of a closed writing instrument into a writing tip characterized in that in the ink introducing tube, a plurality of protrusions are formed from the inner peripheral surface thereof toward the center so as to exert strong capillary action and are extended in the axial direction, and a central space surrounded by the free ends of the plurality of protrusions is formed with such a cross sectional area that would make the capillary action difficult to take place therein, over the entire length of the ink introducing tube.
According to a second aspect of the present invention, the plurality of protrusions are formed having the respective lengths of long and short protrusions oriented toward the central portion being aligned with each other so that substantially the same capillary action can be exerted between the plurality of protrusions even as they come closer to the central space of the ink introducing tube.
According to a third aspect of the present invention, the intervals between the plurality of protrusions are set to approximately 10 to 100 microns and transverse distances therebetween in the central space are set to approximately 100 to 1000 microns.
According to a fourth aspect of the present invention, an ink tank is provided inside a writing instrument shaft portion; the ink tank is communicated with a writing tip located at the forward end of the writing instrument shaft portion through an ink introducing tube, the ink introducing tube including axially extended portions with strong capillary action which.are provided along its inner peripheral surface and a cylindrical space with weak capillary action which is formed in its central portion, and the periphery of the portion where the ink introducing tube and the writing tip are connected is surrounded by an inner wick having the capillary action.
With the above-described construction of the ink introducing tube of the present invention, even in the case of ink having a slightly high viscosity, it can be smoothly replaced by the outside air to allow smooth supply of the ink from the ink tank to the writing tip. Further, a writing instrument incorporating the ink introducing tube of the present invention is also expected to enable smooth writing.